Circular waveguide mode filter and breakdown switch device, utilizing resonant iris



April 9, 1963 Filed Jan. 13, 1960 R. M. WALKER 3,085,213 CIRCULARWAVEGUIDE MODE FILTER AND BREAKDOWN SWITCH DEVICE. UTILIZING RESONANTIRIS 3 Sheets-Sheet 1 BY Common Mounting With Separate Iris Mode FiltersWhich Switch As 'T-R" Devices.

IN V EN TOR.

RICHARD M. WALKER ATTORNEY April 9, 1963 R. M. WALKER CIRCULAR WAVEGUIDEMODE FILTER AND BREAKDOWN SWITCH DEVICE, UTILIZING RESONANT IBIS FiledJan. l5, 1960 3 Shee ts-S he et 2 IN VEN TOR.

RICHARD M. WALKER AT TORN EY Apnl 9, 1963 R. M. WALKER CIRCULARWAVEGUIDE MODE FILTER AND BREAKDOWN SWITCH DEVICE, UTILIZING RESONANTIRIS Filed Jan l5, 1960 5 SheetsSheet 3 FIG. IO

FIG. l2

FIG.

INVENTOR.

RICHARD M. WALKE ATTORNEY United States Patent 3,085,213 CIRCULARWAVEGUIDE MODE FELTER AND BREAKDOWN fiWITCH DEVICE, UTELHZKNG RESQNANTIRIS Richard M. Walker, Boston, Mass, assignor to Micro- WaveAssociates, lino, Burlington, Mass, a corporation of Massachusetts FiledJan. 13, 1960, Ser. No. 2,217 17 Claims. (Cl. 3337) This inventionrelates in general to circular waveguide switch devices, and moreparticularly to switch and duplexing devices for circular waveguidesystems intended for operation in the TE mode.

As is well known, a circular Waveguide operated in the TE mode has theunique and important advantage that its attenuation is appreciably lowerthan that of a rectangular waveguide and decreases with increasinginternal diameter of the waveguide. One ditficulty, however, is that ina waveguide of diameter just large enough to support the TE mode fourother modes will also propagate, namely, the T13 TM TE and TM modes, andin a waveguide of larger diameter additional, higher order, modes willpropagate. Due to this difiiculty, the adoption and use of circularwaveguide systems operated in the TE mode has been delayed. By contrast,rectangular waveguide systems operated in the TE mode enjoy theadvantage of operation in the fundamental mode, and the design ofcomponents for such systems is accordingly less diificult, with theresult that rectangular waveguide systems are more extensively used thancircular waveguide systems nothwithstanding the recognized advantages ofthe latter.

It is an object of this invention to provide a circular waveguideswitching device for operation in the TE mode. It is another object ofthe invention to provide such a switching device which is capable ofoperation in association with circular waveguides having higher powercapabilities and lower loss characteristics than correspondingcomponents in conventional rectangular waveguide form. It is a furtherobject of the invention to provide such a switching device which will beoperable over a broad band frequency spectrum. Further objects are toprovide such a switching device which is of a readily reproducibledesign, lends itself to fabrication by known production techniques, isrugged in structure, and requires no unusual material, and is readilyadaptable for use in circular waveguide duplexers, balanced duplexers,and other circular waveguide circuits. A general object of the inventionis to advance the state of the art of circular waveguide transmissionsystems operable in the TE mode.

According to the invention, there is provided in general a TE modecircular waveguide gas discharge switching device, comprising a sectionof circular waveguide of internal diameter sufficiently large topropagate the TE mode, and transversely mounted in this waveguidesection intermediate its ends an electrically conductive disc in whichat least four radially directed slots are symmetrically arrayed, eachslot being located between the center and the edge of the disc, andbeing elfectively hermetically sealed by an electromagnetic wavepervious gas impervious dielectric material. One such disc having itsslots disposed in an appropriate gas hermetically sealed in the vicinityof the slots, or two such discs located a known distance apart andhaving a region filled with such gas surrounding their slots and betweenthem, may comprise a switch cell which is useful, for example, as a TRcell or a Pre TR cell. Each slot is dimensioned to couple through itmicrowave energy, in a prescribed frequency range, and with like phaseand amplitude changes, which energy has a voltage field componenttransverse to "ice the long slot dimension in the plane of the disc, andto break down electrically by discharge within the gas fill transverseto the long dimension in the plane of the disc when the magnitude ofthis voltage exceeds a prescribed value. Two such waveguide sections,each provided with such a switch cell, are coupled on each side to a TEmode circular waveguide hybrid junction or 3 db directional coupler, tocomprise a balanced duplexer. In a preferred embodiment of such abalanced duplexer the two waveguide sections are parallel and the switchcells lie in the same plane transverse to both sections. Structurally,the switch cells may be fabricated in a single body and further circularwaveguide sections of the same diameter may be attached to this body.

Additional objects and features of the invention will be made apparentin the following description of a preferred embodiment. This descriptionrefers to the accompanying drawings, wherein:

FIG. 1 is a plan view of a switch device according to the invention;

FIG. 2 is a section along line 2-2 of FIG. 1;

FIG. 3 is an enlarged fragmentary view showing a detail of FIG. 2;

FIGS. 4 to 8, inclusive, illustrate the operation of switch devicesaccording to FIG. 1;

FIG. 9 illustrates a balanced duplexer;

FIG. 10* is a section along line 1010 of FIG. 9;

FIG. 11 is a cross-sectional view of a switch device employing only onewindow disc; and

FIG. 12 is a cross-sectional view of another switch device employingonly one window disc.

Referring now to FIGS. 1 and 2, the switch device there illustrated isintended to function as a dual circular waveguide TR or Pre TR cell. Abody 10 is circularly apertured at 11 and 12 to provide two shortsections of circular waveguide. As is shown in FIG. 2, the first-namedshort section 11 has first and second window discs 13 and 14 mountedacross its ends, resting on shoulders 15 and 16, respectively, providedat each end. The second-named short section 12 is similarly fitted, andits structure will not separately described, it being understood thatthe description of the structure of the first-named short section 11 andelements fitted to it is applicable to both sections and the respectiveelements fitted to them.

As exemplified by the first window disc 13, each disc is provided with aplurality of radially directed slots, 17.1, 17.2, 17.3, 17.4, 17.5, 17.6and 17.7. Each slot constitues an iris opening designed to be resonant(i.e., transmit substantially all the incident TE mode power) at thedesired resonant frequency, and to maintain good mode purity in thewaveguide in the unfired condition as will presently be described. Thenumber m of slots in each window disc is such that the TE mode will notbe propagated in the circular waveguide being used, where m=2n, atleast, for the highest mode to be suppressed; while seven slots in eachwindow disc are shown in FIG. 1, under certain conditions a minimumnumber of four slots will suflfice, as will be explained below.Preferably, all the slots in a given window disc have equal couplingvalues, for phase and amplitude, in order to prevent excitation ofsub-multiples of the TE mode (m/Z, m/3, etc.) and TM modes. The windowdiscs may be made of a metal (such as Kovar) having a coefficient ofexpansion substantially equal to that of glass, to which a suitableglass for TR cell windows can be sealed. FIG. 2 shows first and secondglass discs 18 and 19 sealed over the outer surfaces of the first andsecond window discs 13 and 14, respectively. The enlarged fragmentaryview in FIG. 3 shows the first glass disc 18 covering the first slot17.1 in the first window disc '13. The window discs 13 and 14 are, forexample,

suitably plated and soft soldered, and thereby hermetically sealed inthe respective openings of the short waveguide section 11. Other formsof hermetically sealed iris diaphragms may be employed, if desired; forexample, those constructed according to the techniques disclosed in thecopending application of the present inventor and another, Serial No.657,585, filed May 7, 1957. The interior of each short waveguide section11 and 12 is evacuated and filled with a suitable gas (not shown) forefficient TR or Pre TR action. The gas fill and pressure are accordingto known TR tube techniques. Under these conditions, when the magnitudeof the voltage across a coupling slot (i.e., transverse to the longdimension of the slot in the plane of the disc) due to incident powerexceeds a given value, the slot is fired, and a discharge is formedbehind the slot (i.e., on the side away from the glass disc sealing it)to form effec tively a short circuit across the waveguide section due tothe simultaneous'firing of all the slots in a given window disc. Thelength of each assembly, from the first window disc 13 to the secondwindow disc 14, is approximately one quarter wavelength of the TE modein the respective short circular waveguide section, to provide maximumbandwidth for a given window design (for low-level operationi.e., gasnot ionized).

The design and operation of the respective window discs is explainedwith the aid of the schematic illustrations of FIGS. 4 to 8, inclusive.Each of these figures schematically represents a window disc 23' havingfour slots 24. 1, 24.2, 24.3 and 24.4 radially disposed andsymmetrically arrayed in it, the long dimension of each slot lyingbetween the center and periphery or edge of the disc. In such asymmetrical array, the long dimensions of any two successive or adjacentslots (e.g., 24.1 and 24.2) are orthogonally related in the plane of thedisc. When the slots are excited by microwave energy incident at oneside of the window disc 23 in the TE mode, the electric field lineconfiguration of which is circular as is illustrated by the circularline 25 in FIG. 8, each slot has impressed across it a component of theelectric field of said energy which is directed transversely to the longdimension of the slot in the plane of the window disc 23; furthermore,these components are directed in the same direction around the center ofthe disc, for example, clockwise, as is indicated by the arrows 25.1,25.2, 25.3 and 25.4 (hereinafter called field vectors) drawn across theslots 24.1, 24.2, 24.3 and 24.4, respectively, if the TE mode field line25 is directed clockwise. If the slots are designed to couple identicalincrements of energy applied to them with equal attenuation and phasechange effects, the phase front and relative amplitude distribution overthe front of a wave incident at one side of the window disc 23 will bereproduced essentially unaltered on the other side of the disc by theenergy coupled through the slots, and the four-slot array excited as inFIG. 8 by TE mode energy applied at one side of the window disc 23 willgenerate the same mode at the other side of the disc with good modepurity, as will be explained with reference to FIGS. 4 to 7, inclusive.

FIG. 4 shows electric field lines 26.1, 26.2 and 26.3 of the TE mode,and with their respective arrow heads these lines indicate aninstantaneous electric field disposition in a plane parallel to thewindow disc 23. It is assumed that the four slots have been excited byTE mode energy as in FIG. 8. The first slot 24.1 is excited in theproper phase to couple with the electric field of the TE mode, since itsfield vector 25.1 is in phase with the left-hand field line 26.1. It isapparent, then, that if the disc 23 comprised only one slot 24.1 theincidence of TE mode energy at one side of it might result in thegeneration of TE mode energy on the other side of the disc by energycoupled through this single slot. However, the third slot 24.3 has itsfield vector 25.3 180 out of phase with the TE mode field when the firstslot 4 24.1 is in phase with that field, as is indicated by the fieldvector 25.3 being directed oppositely to the righthand field line 26.2of the TE mode. Thus, the two opposite slots 24.1 and 24.3 cooperate toprevent the generation of TE mode energy when they are excited by TEmode energy. The remaining two slots 24.2 and 24.4 have their fieldvectors 25.2 and 25.4 directed across the maximum TE mode field line26.3, so that they do not contribute to the generation of the TE mode.The same conclusion can be proved from an analysis of other orientationsof the instantaneous TE mode pattern relative to this four-slotconfiguration.

In FIG. 6 the electric field lines 27.1, 27.2, 27.3 and 27.4 and therespective arrow heads on them represent an instantaneous electric fieldconfiguration of the TE mode in a given plane parallel to the disc 23(i.e., transverse to a circular waveguide in which the disc 23 may bemounted). Here it is clear from the disposition of the field vectors25.2 and 25.4 of the two opposed slots 4.2 and 24.4, respectively, inphase with the T2321 mode field lines 27.2 and 27.4, respectively, thata single pair of slots having their long dimensions lying along adiameter of the window disc can excite the T5 mode upon being themselvesexcited by the TE mode. The addition of another pair of slots 24.1 and24.3 at right angles to the first pair provides a pair of field vectors25.1 and 25.3 which are simultaneously out of phase with the electricfield of the TE mode as represented by the field lines 27.1 and 27.3 inthe vicinity of these slots. There results a four-slot configurationwhich, when excited by the TE mode, is constrained to generate only theTE mode from the energy coupled through the slots, and does not generatethe TE or the TE mode.

It should be noted that fewer than four slots will not provide'thisproperty, and that if the slots which mutually oppose each otherrelative to any of these two undesired modes fail to oppose each otherequally, a certain amount of the unwanted mode will be generated andpropagated in following circular waveguides unless subsequent steps aretaken to eliminate it. Hence, a symmetrical array of equally fed slots,having equal coupling coetficients and phase change characteristics withrespect to the TE mode, is a preferred arrangement.

The TM field would not be excited by the four slots of the disc 23, asis apparent in FIG. 5. In one plane across the TM mode configuration,the electric field lines 28 are directed radially, as illustrated inFIG. 5, and hence are orthogonally related to all the field vectors25.1, 25.2, 25.3 and 25.4 of the slots which are due to the TE mode. Inanother plane (not shown) across the TM mode configuration the electricfield lines are perpendicu- 'lar to the disc 23 and concentrated in thecenter region 23.1 shown by a dotted circle in FIG. 5. Again theelectric field of the TM mode when so disposed will not be excited bythe field vectors across the slots due to the TE mode.

The TM mode has an instantaneous electric field configuration in a planetransverse to its direction of propagation as is shown in FIG. 7 by theelectric field lines 29, 29.1, 29.2, 29.3, 29.4, 29.5, 29.6, 29.7 and29.8. As in the case of the T13 mode, any pair of opposite and parallelslots, 24.1 and 24.3, for example, lying along the same diameter of thedisc 23, serve to inhibit the generation of the TM mode, due to the factthat their electric field vectors 25.1 and 25.3 resulting from the TEmode are in phase opposition with respect to the electric field of theTM mode; where one field vector (e.g., 25.1) tends to favor generatingthe TM mode, by being in phase with its field as represented by a fieldline 29.1 in the vicinity of the first slot 24.1, the other field vector(e.g., 25.3) opposes the establishment of the field of this mode bybeing opposite to it as represented by the field line 29.3 in thevicinity of the other slot 24.3. The TM mode electric field is directedperpendicular to the disc 23, or is without direction, in the vicinityof the other pair of slots 24.2 and 24.4 in the. disc, so that theseslots cannot contribute to the TM mode.

It is thus seen that a four-slot configuration in a window disc orpartition 23, like the configuration illustrated in FIG. 8, for example,can serve to couple the TE mode across the partition without excitingany of the lower order modes, (TE TM TE or the degenerate mode (TM in awaveguide which is of large enough diameter to propagate the TE mode. Ifa larger diameter waveguide is used, additional slots providing an arrayof slots which are symmetrically arranged and of equal couplingcapability with respect to the TE mode can be used to inhibit theexcitation of higher order modes as well. Thus, the seven-slotconfiguration shown in FIG. 7

1 will inhibit the generation of the TE mode as well as the foregoingmodes, and will couple the TE mode with good mode purity. A symmetricalsix-slot configuration (not shown) could also accomplish this result.The seven-slot configuration is useful in the case where the slots donot have identical coupling characteristics, in that for such cases thisconfiguration will minimize the possibility of exciting unwanted modesbetween the TE and the TE modes. In such a case, there may also be anunbalance among the slots relative to the TE mode, which can cause theTE mode to be excited from incident TE mode energy, and it will then berequired to take other measures to eliminate this single unwanted (TEmode. Referring to FIGS. 1 and 2, this can be done by axially staggeringthe two window discs 13 and 14 by of a revolution, in cases where twowindow discs are used.

FIGS. 9 and illustrate a circular waveguide balanced duplexer using theTE mode. The body 10 containing two TR cells as shown in FIGS. 1, 2 and3 has first and second circular waveguides 33 and 34 collinearly coupledto its opposite sides 31 and 32, respectively, in register with thefirst circular opening 11 therein, and third and fourth circularwaveguides 35 and 36 similarly coupled to it in register with the secondcircular opening 12 therein. There results a structure comprising twoparallel adjacent circular waveguides 33, 34 and 35, 36, in each ofwhich one of the TR cells which is supported in the body 10 istransversely mounted. When T13 mode energy is introduced at one end ofeither of these waveguides, it is coupled through the TR cell thereinwith good mode purity to the other end, unless it is of sufiicientlyhigh level to fire the iris openings 17.1417 .7, inclusive, in whichcase it is reflected.

The two elements 41 and 42 on one side 31 of the body 10, and the twoelements 43 and 44 on the other side 32 of the body 10 represent hybridjunctions or 3 db directional couplers cross connecting the two circularwaveguides 33, 35 and 34, 36 on each side of the TR cells, as is done inknown rectangular waveguide balanced duplexer circuits, to provide thecomplete circular waveguide balanced duplexer circuit. Such couplers perso are not part of the present invention. They can be realized, forexample, with pairs of rectangular waveguide coupling links which arewrapped around the circular waveguides, each link being constructedaccording to US. Patent No. 2,766,432 to Walker, the present inventor,or US. Patent No. 2,676,306 to Lanciani. If either of these patentedconfigurations is used, the end reflectors there shown in the circularwaveguide will be omitted, and two (or more) such coupling links will beemployed, spaced along the circular waveguides 33, 35 on one side 31 ofthe body 1% in the one case, and 34, 36 on the other side 32 of the bodyit in the other case, to provide the desired directivity. The number ofcoupling links required in either case is determined by the couplingratio which can be achieved in a single link and the desired bandwidthof the resulting 3 db coupler. As is stated in the patent to Walker,coupling in an individual link can be increased at the expense ofbandwidth. The rectangular waveguide sections 41.1, 42.1, 43.1 and 44.1,interconnecting each pair of coupling links will propagate the dominantor TE rectangular waveguide mode.

While certain patented coupling configurations have been suggested forthe 3 db directional couplers required to achieve the circular waveguidebalanced duplexer illustrated in FIGS. 9 and 10, it will be apparent tothose skilled in the art that other couplers or hybrid junctions may beemployed.

Embodiments of the invention employing only one window disc may beconstructed according to FIG. 11 or FIG. 12. Each of these figuresillustrates an embodiment of the invention in cross section taken as inFIG. 2, showing the body ill and one of the short sections 11 ofcircular waveguide therein, and a single window disc 13 mounted in theshort section 11. In FIG. 11 the window disc 13 is mounted approximatelyin the center of the circular waveguide section 11, and glass discs and52, mounted in suitable metal-to-glass sealing rings 51 and 53,respectively, hermetically seal the respective openings of the waveguidesection. In FIG. 12 the window disc 13 is mounted near one of theopenings, in contact with one of the windows 5% In either case, asuitable gas fill (not shown) is provided in the cell for efficient TRor Pre TR action.

The embodiments of the invention which have been illustrated anddescribed herein are but a few illustra tions of the invention. Otherembodiments and modifications will occur to those skilled in the art. Noattempt has been made to illustrate all possible embodiments of theinvention, but rather only to illustrate its principles and the bestmanner presently known to practice it. Therefore, while certain specificembodiments have been de-' scribed as illustrative of the invention,such other forms as would occur to one skilled in this art on a readingof the foregoing specification are also within the spirit and scope ofthe invention, and it is intended that this invention includes allmodifications and equivalents which fall within the scope of theappended claims.

What is claimed is:

1. TE mode circular waveguide switch comprising a section of circularwaveguide of substantially uniform internal diameter sufficiently largeto propagate the TE mode, first and second electrically conductivediscs, transversely mounted in said waveguide a known distance apart, atleast four radially directed slots each of which is electricallysymmetrical about its long dimension and has long edges confronting eachother, said slots being symmetrically arrayed in each disc, the longdimension of each slot being substantially smaller than the radius ofthe disc in which it is arrayed, each slot being located between thecenter and the edge of the disc in which it is arrayed and beingdimensioned to couple therethrough microwave energy in a prescribedfrequency range which has a voltage field component transverse to thelong slot dimension at said disc, and to break down across said longdimension when the magnitude of said voltage across said slot exceeds aprescribed value the center portion of each disc being free ofperforation by any of the slots arrayed in said disc, andelectromagnetic wave pervious gas impervious means closing each slot andhermetically sealing the space in said waveguide section between saiddiscs.

2. Switch according to claim 1 in which each of said slots couples anidentical quantity of said energy at said frequency.

3. Switch according to claim 1 in which said known distance between saidfirst and second discs is substantially one-quarter wavelength of the TEmode in Said section of circular waveguide.

4. Switch according to claim 1 in which each of said slots is resonantat a frequency in said range.

5. Switch according to claim 3 in which each of said lots couples anidentical quantity of said energy at said requency.

6. TE mode circular Waveguide switch comprising a section of circularwaveguide of substantially uniform internal diameter sufficiently largeto propagate the TE mode, first and second electrically conductive discstransversely mounted in said waveguide a known distance apart, fourradially directed slots each of which is electrically symmetrical aboutits long dimension and has long edges confronting each other, said slotsbeing symmetrically arrayed in each of said discs, the long dimension ofeach slot being rectangularly disposed relative to the long dimension ofeach adjacent slot in the same disc and being substantially smaller thanthe radius of said disc, said slots each being positioned between thecenter and the edge of the disc in which it is arrayed, each slot beingdimensioned to couple therethrough microwave energy in a prescribedfrequency range which has a voltage field component transverse to thelong slot dimension at said disc, and to break down across said longdimension when the magnitude of said voltage across said slot exceeds aprescribed value the center portion of each disc being free ofperforation by any of the slots arrayed in said disc, andelectromagnetic wave pervious gas impervious means closing each slot andhermetically sealing the space in said waveguide section between saiddiscs.

7. TE mode circular waveguide switch circuit comprising first and secondcircular waveguides each of internal diameter sufficiently large topropagate the TE mode, an electrically conductive disc transverselymounted in each of said waveguides, at least four radially directedslots each of which is electrically symmetrical about its long dimensionand has long edges confronting each other, said slots beingsymmetrically arrayed in each of said discs, the long dimension of eachslot being su stantially smaller than the radius of the disc in which itis arrayed, each slot being located between the center and the edge ofits disc whereby the center portion of said disc is not perforated byany of said slots, electromagnetic wave pervious gas impervious meansclosing each slot, each slot being dimensioned to couple therethroughmicrowave energy in a prescribed frequency range which has a voltagefield component transverse to the long slot dimension at said disc, andto break down across said long dimension when the magnitude of saidvoltage across said slot exceeds a prescribed value, and hybrid couplingmeans interconnecting said waveguides on each side of said discs.

8. Circuit according to claim 7 in which said first and secondwaveguides are parallel to each other, and said discs are in a commonplane transverse to both of said waveguides.

9. Circuit according to claim 8 in which a single flat body supportssaid discs, and said waveguides are each in two sections connectedcollinear'ly to opposite sides of said body.

10. TE mode circular waveguide switch circuit comprising first andsecond circular wave guides each of internal diameter sufiiciently largeto propagate the TE mode, first and second electrically conductive discstransversely mounted a known distance apart in each waveguide, at leastfour radially directed slots each of which is electrically symmetricalabout its long dimension and has long edges confronting each other, saidslots being symmetrically arrayed in each disc, the long dimension ofeach slot being substantially smaller than the radius of the disc inwhich it is arrayed, each slot being located between the center and edgeof its disc, electromagnetic wave pervious gas impervious means sealingeach slot and hermetically sealing the space between the first andsecond discs in each of said waveguides, each slot being dimensioned tocouple therethrough microwave energy in a prescribed frequency rangewhich has a voltage field component transverse to the long slotdimension at said disc, and to break down across said long dimensionwhen the magnitude of said voltage across said slot exceeds a prescribedvalue the center portion of each disc being free of perforation by anyof the slots arrayed in said disc,

8 and hybrid coupling means interconnecting said waveguides on each sideof said discs.

11. Circuit according to claim 10 in which said first and secondwaveguides are parallel to each other, said first discs in eachwaveguide are located in a first common plane and said second discs ineach waveguide are located in a second common plane, and said planes areparallel to each other and transverse to both of said waveguides.

12. Circuit according to claim 11 in which a single flat body havingopposite plane sides spaced substantially said known distance apart andapertured in two places to mate with the internal cross section of saidwaveguides supports a first and a second of said discs at the oppositesides, respectively, of each aperture, and said waveguides are each intwo sections connected collinear-1y to opposite sides of said body inregister with one of said apertures.

13. Circuit according to claim 12 in which the hermetic sealing meansare a sealing disc over each of said apertures outside of each of saiddiscs.

14. TE mode circular waveguide switch circuit cornprising first andsecond circular waveguides each of internal diameter sufliciently largeto propagate the TE mode, first hybrid coupling means interconnectingsaid waveguides at a first region of each, said coupling meanscomprising rectangular waveguide coupling links at each said region forinterchanging TE mode energy in a circular waveguide with dominant modeenergy in a rectangular waveguide and rectangular waveguide meansinterconnecting said coupling links between said circular waveguides,second hybrid coupling means similar to said first hybrid coupling meansinterconnecting said circular waveguides at a second region of each andan iris means in each circular waveguide intermediate said first andsecond regions, each iris means being adapted to pass TE mode energy andto prevent passage of lowerorder circular waveguide modes, each irisbeing simultaneously adapted to break down in the presence thereat of TEmode energy having a voltage exceeding a prescribed value.

15. Switch circuit according to claim 14 in which each of said irismeans comprises electrically conductive disc means transversely mountedin said circular waveguide, said disc means having radially-directedelongated slot apertures of length substantially less than the radiusthereof located between the center and the periphery thereof so that thecenter portion is devoid of any aperture, each aperture beingelectrically symmetrical about its long dimension, the apertures beingdisposed and dimensioned to pass TE mode energy through said disc meansfrom one side to the other, each slot being dimensioned to break downelectrically across the long dimension thereof in the presence of avoltage exceeding said prescribed value.

16. TE mode circular wave guide switch comprising: a section of circularwaveguide of substantially uniform internal diameter sufficiently largeto propagate the TE mode, an electrically conductive disc transverselymounted approximately in the center of said wave guide section, at leastfour radially directed slots each having a long dimension which issubstantially smaller than the radius of said disc symmetrically arrayedin said disc, each slot being electrically symmetrical about its longdimension and having long edges confronting each other, each slot beinglocated between the center and edge of said disc whereby the centerportion of said disc is not perforated by any of said slots, andelectromagnetic wave pervious gas impervious means electrically sealingeach end of said wave guide section, said slots each being dimensionedto couple therethrough microwave energy in a prescribed frequency rangewhich has a voltage field component transverse to the long slotdimension at said disc, and to break down across said slot when themagnitude of said voltage exceeds a prescribed value.

17. TE mode circular wave guide switch comprising: a section of circularwave guide of substantially uniform internal diameter sufliciently largeto propagate the TE mode, an electrically conductive disc transverselymounted across one end of said Wave guide section, at least fourradially directed slots each having a long dimension which issubstantially smaller than the radius of said disc symmetrically arrayedin said disc, each slot being electrically symmetrical about its longdimension and having long edges confronting each other, each slot beinglocated between the center and edge of said disc whereby the centerportion of said disc is not perforated by any of said slots, andelectromagnetic Wave peiyious gas impervious means electrically sealingeach end of said wave guide section, said disc being in contact With oneof said sealing means, said slots each being dimensioned to coupletherethrough microwave energy in a prescribed frequency range Which hasa voltage field component transverse to the long slot dimension at saiddisc, and to break down across said slot when the magnitude of saidvoltage exceeds a prescribed value.

References Cited in the file of this patent UNITED STATES PATENTS2,197,122 Bowen Apr. 16, 1940 2,586,993 Riblet Feb. 26, 1952 2,691,766Clapp Oct. 12, 1954 2,894,218 Lanciani July 7, 1959 FOREIGN PATENTS256,330 Switzerland Feb. 16, 1949 OTHER REFERENCES Srnullin: MicrowaveD'uplexers (vol. 14 of Radiation Laboratory Series). Published byMcGraw-Hill, New York, 1948. (Pages 102-112 relied on).

1. TE01 MODE CIRCULAR WAVEGUIDE SWITCH COMPRISING A SECTION OF CIRCULARWAVEGUIDE OF SUBSTANTIALLY UNIFORM INTERNAL DIAMETER SUFFICIENTLY LARGETO PROPAGATE THE TE01 MODE, FIRST AND SECOND ELECTRICALLY CONDUCTIVEDISCS, TRANSVERSELY MOUNTED IN SAID WAVEGUIDE A KNOWN DISTANCE APART, ATLEAST FOUR RADIALLY DIRECTED SLOTS EACH OF WHICH IS ELECTRICALLYSYMMETRICAL ABOUT ITS LONG DIMENSION AND HAS LONG EDGES CONFRONTING EACHOTHER, SAID SLOTS BEING SYMMETRICALLY ARRAYED IN EACH DISC, THE LONGDIMENSION OF EACH SLOT BEING SUBSTANTIALLY SMALLER THAN THE RADIUS OFTHE DISC IN WHICH IT IS ARRAYED, EACH SLOT BEING LOCATED BETWEEN THECENTER AND THE EDGE OF THE DISC IN WHICH IT IS ARRAYED AND BEINGDIMENSIONED TO COUPLE THERETHROUGH MICROWAVE ENERGY IN A PRESCRIBEDFREQUENCY RANGE WHICH HAS A VOLTAGE FIELD COMPONENT TRANSVERSE TO THELONG SLOT DIMENSION AT SAID DISC, AND TO BREAK DOWN ACROSS SAID LONGDIMENSION WHEN THE MAGNITUDE OF SAID VOLTAGE ACROSS SAID SLOT EXCEEDS APRESCRIBED VALUE THE CENTER PORTION OF EACH DISC BEING FREE OFPERFORATION BY ANY OF THE SLOTS ARRAYED IN SAID DISC, ANDELECTROMAGNETIC WAVE PERVIOUS GAS IMPERVIOUS MEANS CLOSING EACH SLOT ANDHERMETICALLY SEALING THE SPACE IN SAID WAVEGUIDE SECTION BETWEEN SAIDDISCS.